We saw our mother waiting for us at the door.
我们瞧见老妈在门那里等着我们.
waiting for us at the door,动名词形式作宾语补足语,承接前面及物动词（也是感官动词）see（saw系see的一般过去式）指向宾语our mother后,以补充完整,且与our mother构成复合宾语.
若考虑宾语从句,需还原完整：
We saw (that) our mother was waiting for us at the door.
由that引导,从句为our mother was waiting for us at the door.作主句的宾语成分；主句主语we,谓语动词saw We saw our mother waiting for us at the door.
我们瞧见老妈在门那里等着我们.
waiting for us at the door,动名词形式作宾语补足语,承接前面及物动词（也是感官动词）see（saw系see的一般过去式）指向宾语our mother后,以补充完整,且与our mother构成复合宾语.
若考虑宾语从句,需还原完整：
We saw (that) our mother was waiting for us at the door.
由that引导,从句为our mother was waiting for us at the door.作主句的宾语成分；主句主语we,谓语动词saw